Asphalt roadways are generally constructed by laying heated paving material, such as bituminous aggregate mixtures or asphalt onto a roadbed. After the heated asphalt is laid, it is typically spread, leveled and compacted such that upon cooling, a road with a uniform, smooth surface that is passable by vehicles is achieved. In order to spread the heated asphalt, a paving machine, known as a screed, may be used. Such screeds can be pulled by a tractor, truck or the like or can be self-propelled. The truck or the tractor supplies the asphalt and the screed then heats, vibrates and manipulates the asphalt into a smooth uniform surface. A screed generally employs a screed assembly having one or more separable screed units.
The screed may represent a significant portion of overall machine mass, and may thus have a substantial effect on machine braking performance. In particular, a tractor or other pulling machine coupled to multiple filled screeds may have difficulty meeting minimum stopping time/maximum stopping distance requirements due to the additional mass of the screeds and their contents. Therefore, additional braking capabilities beyond those provided by the decelerations of the tractor or truck may be needed.
It is possible to extract additional energy from the machine motion via a hydraulic drive circuit linked to the machine wheels. In this arrangement, the hydraulic fluid would absorb the excess energy not extracted by the decelerations, slowing the machine, with the excess energy then being dissipated from the hydraulic fluid via a radiator or other means. However, the heat cycling of the hydraulic fluid may negatively impact fluid life and may also at least temporarily degrade fluid performance, leading to reduced performance as well as a requirement for more frequent fluid replacement. Moreover, the hydraulic fluid may have a maximum heat capacity that is less than that required to effectively stop the machine under more challenging circumstances. In short, mechanisms for extracting and dissipating excess paving machine speed have not, to date, been entirely acceptable.
It will be appreciated that this background section was created by the inventors for the reader's convenience, and is meant to discuss problems and solutions noted by the inventors, not to discuss or explain prior art. Thus the inclusion of any problem or solution in this section is not an indication that the problem or solution is prior art.